Tablets coated with aqueous resin dispersions

ABSTRACT

Coated tablets are prepared by applying to a core of active material, at least one layer of a coating composition made up of a film forming aqueous synthetic resin dispersion and from 2-50% by weight of a water or alkaline soluble material and thereafter permitting the coating composition layer to dry. The resulting coated tablet has a core surrounded by a continuous porous matrix of synthetic resin formed from the aqueous dispersion which is insoluble in water and insoluble in the gastrointestinal tract. The pores of the continuous resin matrix are filled with a discontinuous particulate material which is water or alkaline soluble. The coated tablet initially is air and moisture tight.

RELATED APPLICATIONS

This is a division of application Ser. No. 463,216, filed Apr. 22, 1974,now U.S. Pat. No. 3,935,326 which is in turn a Continuation-in-Part ofapplication Ser. No. 44,557, filed June 8, 1970, now abandoned, which isin turn a division of application Ser. No. 740,058 filed June 26, 1968,now abandoned.

BACKGROUND

This invention relates to coating compositions for tablets. Moreparticularly this invention relates to tablet coating compositions whichcan be applied in thin layers, are impervious to heat and which result,as desired, in tablet coatings which are either water soluble or areonly soluble in the small intestine.

In addition to the sugar coatings for dragees, which have been known formany years, recently several synthetic resin coating agents for tabletshave been developed which in comparison with dragees, have the advantagethat a satisfactory coating for tablets can be obtained withsubstantially less and thinner layers. Depending on the nature of thesynthetic resins used, there are obtained coatings which are eitherwater soluble or are resistant to gastric juices (cf. German Pat. Nos.1,056,786 and 1,228,757).

A disadvantage of these synthetic resin coatings is that they have to beapplied to the tablet cores in the form of their solutions in organicsolvents, such as, for example, acetone, alcohol, chloroform, carbontetrachloride and the like. Although these solvents evaporate veryreadily and, therefore, the finished coatings are obtained in acomparatively short period of time, these coating agents possess manysignificant disadvantages. These disadvantages include the following:

1. Large amounts of solvents are needed as the solids content in thesecoating agents usually cannot be much more than 20% due to the viscosityrequirements;

2. The solvents, which are expensive in comparison with water, areeither completely lost or can only be recovered by the use of veryexpensive apparatus;

3. Because of the toxicity of the solvent vapors, special safetymeasures must be provided in the working areas in order to protectpersonnel;

4. Most organic solvents are inflammable and mixtures of solvent vaporswith air are explosive so that it is necessary to use expensiveapparatus which is secure against possible fire and explosion.

In German Pat. No. 1,229,678, it has been proposed to apply moltenpolyethylene glycol to pre-heated tablet cores. This process admittedlyavoids the use of solvents but then it necessitates the preparation ofhot melts. Temperatures of up to 130° C are unusually high for use inthe production of tablet coatings. All tubes, spray nozzles and the likeof the involved apparatus, must be heatable in order to avoid asolidification of the polyethylene glycol inside of or on the surfacesof the apparatus.

Furthermore, the tablets have to be pre-heated which is something to beavoided, if possible, particularly in the case of heat sensitive activematerials. A further disadvantage of this process is the fact that itcan only be carried out with the use of the polyethylene glycols which,as are known, have a particularly unpleasant taste.

It is accordingly an object of the invention to provide a new field oftablet coating composition which can be applied in thin layers, areimpervious to heat and which as desired, can either be water soluble oronly soluble in the medium found in the small intestine.

It is another object of the invention to provide a method of producingtablet coating compositions of the character indicated.

A further object of the invention is to provide synthetic resin tabletcoatings which do not require the use of organic solvents in eithertheir preparation or deposition.

Still another object is to provide synthetic resin tablet coatingscompositions which can be applied at room temperature and in fairly highconcentrations, i.e., coating compositions which can be easily andsimply applied to tablet cores.

Other objects and various features of novelty and invention will bepointed out or will occur to those skilled in the art from a reading ofthe following specification.

SUMMARY

The present invention provides a process for preparing coated tabletswhich comprises applying to a core of active material at least one layerof a coating composition comprising a film forming aqueous syntheticresin dispersion and from 2-50% by weight of a water or alkaline solublematerial and thereafter permitting the coating composition layer to dry.

The coated tablet produced by the process of the invention can becharacterized as including a core of active material which is soluble inthe gastrointestinal tract and surrounded by a continuous porous matrixof synthetic resin formed from the film forming aqueous synthetic resindispersion. The continuous resin matrix is insoluble in water and isthus insoluble in the gastrointestinal tract. The pores of the matrixcontain from 15 to 600 %, based on the weight of the dried resin (film)matrix, a discontinuous or particulate material which is water oralkaline soluble. The coated tablet is initially air and moisture tight,but upon exposure to water or aqueous alkaline, the discontinuoussoluble material in the continuous resin matrix will be dissolved fromthe pores thereof. Depending on the nature of the soluble, discontinuousmaterial, the continuous resin matrix will remain intact becomingsufficiently porous thereby allowing the core of active material todiffuse out through the porous resin matrix, or will be torn apart, inthe gastrointestinal tract.

DESCRIPTION OF THE DRAWING

The present invention will be more fully understood from the followingdescription taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a schematic flow diagram with appropriate legends illustratinga preferred procedure for carrying out the process of the invention;

FIG. 2a is an enlarged cross-sectional view of a tablet coated accordingto the present invention; and

FIG. 2b is an enlarged microscopic view of a tablet coating formedaccording to the present invention.

DESCRIPTION

Film-forming aqueous synthetic resin dispersions are known from thepaint technology field and are, in general, applied to a stationarysubstrate, movement or touching of the coated surface having to becarefully avoided until the drying is complete. Consequently, it was tohave been expected that upon application of such synthetic resindispersions to tablet cores moving about in a drageeing kettle, smoothsurfaces would not be obtained but rather non-uniform, cracked coatingswhich would either stick to the walls of the kettle or would result inthe tablet cores clumping together. These unsatisfactory results were tohave been expected, particularly since the rubbing together of thetablet surfaces and the increasing concentration of the dispersions upondrying would give rise to the fear of premature coagulation andbreakdown of the dispersion. In point of fact, the commerciallyavailable aqueous synthetic resin dispersions only result in theproduction of coherent, smooth surfaces when they additionally containcertain amounts of fillers.

According to the present invention, it is necessary to add materialswhich are water soluble or are soluble in alkaline solutions, whichmaterials can be dissolved either by the gastric juices or by thealkaline juices in the small intestine, so that from the synthetic resinfilms which are initially completely air and moisture tight and are,therefore, also stable under tropical conditions, there are formedcoatings which are permeable to the active materials present in thetablet cores. These materials which are water soluble or are soluble inalkaline solutions thereby simultaneously also act as the fillers whichare necessary for process technical reasons. However, if desired, otherinsoluble fillers can additionally be added. The amount of theseadditives does not have to be very great. Thus, in accordance with theinvention, it has been found that the use of the additives in an amountin toto of 5-6% is sufficient in order to make the synthetic resindispersions suitable for tablet coatings.

Depending upon the requirements necessary for the particular coatingsinvolved, there are used up to 50% of insoluble fillers and 2-50% of thematerials which are water soluble or soluble in alkaline solutions, inboth cases referred to the amount of aqueous synthetic resin dispersionused. With increasing amounts of the substances which are water solubleor soluble in alkaline solutions, the tablet coatings are more quicklyand intensively attached in the stomach or small intestine and thus giverise to a coating which is sufficiently porous to allow the activematerials present in the tablet cores to diffuse out through thecoating.

When strongly swelling substances, so-called "disintegrating agents" areadded in large amounts to the tablet cores, then it can easily happenthat the porous coating is actually torn apart in the gastrointestinaltract. In this manner, the site and time of the liberation of the activematerial can be varied as desired depending upon the nature and amountof the additives employed. It is, in any case, possible to achievebreakdown and liberation times which are just as short as, or evenshorter than, those of the best known dragees. However, according to thepresent invention, it is also possible to produce tablets having aconsiderably delayed liberation time or with an exclusively entericliberation so that the new tablet coatings have a very wide field ofapplication.

Further advantages of the new coating compositions according to thepresent invention and involving the use of aqueous dispersions ofsynthetic resins, are the avoidance of the use of organic solvents, theability to work at ambient temperature and the relatively highproportion of solids. Thus, in contradistinction to solutions, theresultant viscosity of the aqueous synthetic resin dispersions permit asatisfactory working even in the case of concentrations of between 30and 60%. As a result, it is possible to considerably shorten the dryingtimes necessary for the removal of the water, which drying times arelonger and require the use of more heat where organic solvents have beenemployed.

The application of the additive-containing aqueous synthetic resindispersions according to the present invention can be carried out notonly manually, as by pouring the coating compositions onto the tabletcores but also by spraying the same onto the cores using for thespraying semiautomatic or fully automatic devices. The application ofthe new coating compositions according to the present invention can becarried out in a particularly easy and simple fashion by means of theautomatic drageeing apparatus described in German Pat. No. 1,247,547,which apparatus is manufactured under the mark "ZDS" by Strunck & Co.,Cologne, Germany. When this apparatus is used, it is advantageous towait for a short period of time after application of the coatingcomposition to the moving tablet cores, i.e., until the applied amountof coating composition has been uniformly distributed over the coresbefore proceeding with the drying. Thereafter, drying is carried outwith warm air or, preferably, with air at normal, i.e., room temperatureuntil the cores no longer stick together, but roll smoothly over oneanother. Depending upon the shape and size of the tablet cores, as wellas upon the composition of the coating agent, 5 to 10 coatings areusually sufficient to provide coatings upon the tablet cores whichsatisfy all requirements.

Surprisingly, with the use of the new coating compositions according tothe present invention, it is possible for the first time, to apply,distribute and dry the coating compositions so that it is now no longernecessary, as was previously the case, to apply several layers insuccession onto the tablets. On the contrary, a single, homogeneouscoating results from a continuous application of the coatingcomposition.

As aqueous synthetic resin dispersions for the coating compositionsaccording to the present invention, there can, in principle, be used allpharmacologically compatible, film forming aqueous dispersions. Thus,for example, there can be used the commercially available dispersions ofpolyvinyl esters, polyvinyl acetals, polyvinyl chloride,butadienestyrene copolymers, polyacrylic acid esters and the like.

Aqueous synthetic resin dispersions used in the present invention aredurable, milky dispersions of solid particles of synthetic resins havingan average particle size in diameter of from 0.2-3 microns. The aqueousdispersions are similar to natural rubber latex and can be diluted, ifdesired, with water. The dispersions themselves are produced using knownemulsion polymerization techniques.

The continuous porous resin matrix produced according to the presentinvention is formed by evaporating the water from the dispersioncoating. The continuous resin matrix produced is generally clear, havingthe characteristics of a soft or flexible thermoplastic film. Thecontinuous resin matrix are generally soluble in solvents, such asketones, esters and aromatic and chlorinated hydrocarbons, but arecompletely insoluble in water. The continuous resin matrix is alsogenerally regarded as being chemically resistant.

The properties of the tablet coatings produced according to theinvention from aqueous synthetic resin dispersions are controlled by theaddition of water and/or alkaline soluble materials to the aqueousdispersion, the amount of these soluble materials employed in thecontinuous resin coating (also used in conjunction with other inertmaterials as described above) are controlled so as to produce a tabletwith a coating which will become permeable or porous or which willdecompose in the gastrointestinal tract. Relatively small additions ofsoluble materials, for example up to about 50% by weight based on theweight of the dried resin matrix results in a slightly permeable tabletcoating which is desired in the case of so-called retard preparations.Coatings designed to de-compose more readily, for example in thedigestive juices present in the stomach require a larger amount ofsoluble materials, for example up to 600% by weight based on the weightof the dried resin matrix. Coatings for retard preparations which areresistant to gastric juices employ either an alkaline soluble materialin the continuous resin matrix and/or the incorporation of carboxylgroups into the resin matrix via the aqueous dispersion itself.

Prior to the present invention, tablet coating with synthetic resinfilms was carried out using organic solvent coating techniques. Waterhas been used but only to carry out auxiliary functions in conjunctionwith organic solvent coating procedures (cf. Australian Pat. No.268,497). Prior to the present invention, tablet coating with syntheticresins based solely on an aqueous coating technique was not possible.Prior attempts using water soluble film forming resins, such ascellulose derivatives and polyvinyl alcohol were not successful becausethe aqueous coating solution could only contain low concentrations ofthe soluble resin. This resulted in an undesirable water attack on thesurface of the core of active material itself to say nothing of thecomplicated coating and drying techniques themselves.

Contrary to what the art would have expected, the present inventionmakes it possible to coat tablets with synthetic resins using a totallyaqueous system. This is possible because the aqueous resin dispersionscan be used in a highly concentrated form, which means that asubstantially smaller amount of water has to be evaporated to form adried, finished coating. The present invention also employs quick dryingof the coated tablets, such as by the dipping tube method, which resultsin a rapid evaporation of the water which effectively prevents the waterfrom reaching and penetrating into the core of active material.Moreover, because the aqueous resin dispersions form a durable syntheticresin film, soluble auxiliary material, such as described herein can beincorporated into the film or a continuous resin matrix in a controlledmanner.

Thus, it was not believed possible to use a totally aqueous coatingtechnique for producing coated tablets and it was also thought thatunder high mechanical stresses as occur in a tablet coating process thatthe colloidal resin particles would undergo a premature coagulationresulting in a non-uniform and non-coherent coating on the tablet core,especially in the presence of auxiliary materials, such as the water oralkaline soluble materials and filling agents (cf. Hans Reinhard:"Dispersionen Synthetischer Hochpolymerer", part II application, pages8-10). The coating process of the invention also provides processingadvantages from an environmental standpoint. Prior to the presentinvention, the use of organic solvents required elaborate procedures andtechniques to protect the worker and his environment as well as toprevent the expulsion of unwanted solvent vapors into the atmosphere.Because the present invention is based totally on an aqueous dispersioncoating technique, all of these problems are avoided thereby enhancingthe economics and the environmental compatibility of the claimedprocess.

Suitable dispersions are:

a. Mowilith DM 1, manufactured by Hoechst consisting of a 50% aqueousdispersion of a mixed polymerisate of vinylacetate and maleic acidester, characterized by a particle size of 0.3-2 μ, a pH of 4-5, aresistance to cold down to -18° C and comprising polyvinylalcohol asprotective-colloid. The viscosity of the dispersion was determined atambient temperature (20° C) by means of a "Ford-viscosimeter"; nozzle:6mm; time of outflow: 10 seconds.

b. Mowilith DM 20, manufactured by Hoechst consisting of a 50% aqueousdispersion of a mixed polymerisate comprising vinylacetate,characterized by a particle size of 0.2-3 μ and a pH of 4-5. Theviscosity of the dispersion was determined at ambient temperature bymeans of a "Ford-viscosimeter"; nozzle: 6mm; time of outflow: 10seconds.

c. Propiofan 590 D, manufactured by BASF consisting of a 50% aqueousdispersion of a mixed polymerisate comprising vinylpropionate and anon-ionogenic emulsifier, characterized by a pH of 5 to 7 and a particlesize of 0.2-3 μ. The viscosity of the dispersion was determined at atemperature of 20° C by means of a "Ford-viscosimeter"; nozzle: 6mm;time of outflow: 45 seconds.

d. Lutofan 300D, manufactured by BASF consisting of a 50% aqueousdispersion of a mixed polymerisate comprising vinylchloride and anon-ionogenic emulsifier characterized by a pH of about 5 and a particlesize of about 1 μ. The viscosity of the dispersion was determined at atemperature of 20° C by means of a "Ford-viscosimeter"; nozzle: 6mm;time of outflow: 5 seconds.

e. Acronal 14D, manufactured by BASF consisting of a 50% aqueousdispersion of a mixed polymerisate of acrylic-esters and a non-ionogenicemulsifier, characterized by a pH of 5-7 and a particle size of about0.3 μ. The viscosity of the dispersion was determined at a temperatureof 20° C by means of a "Ford-viscosimeter"; nozzle: 6mm, time ofoutflow: 5 seconds.

f. Litex SB 40, manufactured by Chemische Werke Huls consisting of a 50%aqueous dispersion of a mixed polymerisate of 60% styrene, 40% butadieneand a non-ionogenic emulsifier, characterized by a pH of 9-10 and aparticle size of about 0.2 μ. The viscosity of the dispersion wasdetermined at a temperature of 20° C by means of a "Ford-visosimeter";nozzle: 6mm; time of outflow 5 seconds.

Preferred aqueous synthetic resin dispersions in the process of theinvention are dispersions based on polyacrylates. These materials arepreferred because of their physiological compatibility and desirabletoxicological properties. In addition to ACRONAL 14D described above,commercially available polyacrylates can be used. For example EUDRAGIT L30D and EUDRAGIT E 30D, manufactured by Rohm Pharma GmbH., Darmstadt,Germany, can be used as aqueous polymer dispersions for manufacturingrapidly disintergrating film tablets and delayed-release preparationsaccording to the present invention. These two aqueous polymerdispersions are plasticizer-free, acrylic resin dispersions containing30% solids which form a clear, flexible film built-up frompoly(meth)acrylic acid esters. Both films formed from these polymerdispersions are insoluble in water which is a common characteristic toall aqueous synthetic resin dispersions used in the present invention.

Illustrative of the fillers which, for process technical reasons, are tobe added to the dispersions, are talc, chalk, kaolin, maize starch, ricestarch, highly dispersed silicic acid and the like.

As examples of water-soluble materials suitable for incorporation intothe coating compositions, there may be mentioned salts, sugars,polyethylene glycols, polyvinyl pyrrolidones, wherein the polyethyleneglycols can simultaneously act as lubricants and the polyvinylpyrrolidones can simultaneously act as adhesives. Another water solubleadhesive which can, if desired, be added is starch syrup.

Typical examples of water soluble substances for this purpose are sodiumchloride, saccharose, lactose, glucose, sorbitol mannitol,polyethylenglycol 20,000, polyvinylpyrrolidone ("Kollidon 25" from BASF)and polyvinylalcohol ("Mowiol N 30-98" from Hoechst).

As illustrative of the alkali-soluble materials for inclusion withcoating compositions and which are resistant to gastric juices, therecan be mentioned all physiologically compatible acidic solid materials,such as the higher fatty acids, as for example lauric acid, palmiticacid, stearic acid, polyacrylic acid and polymethacrylic acid.

Further additives which, if desired, can be added to the synthetic resindispersions include dyestuffs, colored pigments, flavorings andpreserving agents.

If the final film is to be particularly soft and elastic, thenplasticizers, such a phthalic acid esters, can be also added, preferablyin the form of their emulsions.

For the production of the final mixture, it is advantageous to firststir up the powdered solid materials with demineralized water, as wellas possibly with small amounts of an emulsifying agent and/or a wettingagent in order to provide a suspension, the viscosity of which issimilar to that of the synthetic resin dispersion, and then slowly tomix it with the latter. After a thorough homogenization of the resultantmixture, the composition can be used immediately.

In some cases, it has proved to be advantageous to apply a layer of purepolyvinyl alcohol, polyvinyl pyrrolidone or solid polyethylene glycol tothe tablet cores before the application of the first layer of thecoating composition of the invention. Furthermore, it is, of course,also possible to first apply a coating which is resistant to gastricjuices, followed by the application of further layers of the coatingcomposition according to the present invention. In this manner, thereare obtained tablets from which the active materials are belatedlyliberated in the small intestine and then by slow diffusion.

The finished tablet cores coated with the composition according to thepresent invention, are generally only 5-15% heavier than the originalcores because completely unbroken coatings are obtained when the amountof composition is applied is only about 3% of the weight of the tabletcore. Furthermore, a subsequent polishing or waxing, as in the case ofdragees, is completely unnecessary because the finished synthetic resincoatings have themselves a permanent, silky gloss.

The tablet or pill cores which are coated with the compositions of theinvention can be pharmaceutical in nature, confectionary materials orgum centers.

The following Examples are given for the purpose of illustrating thepresent invention but in no way are to be construed as a limitationthereof.

Referring now to the drawing and in particular FIG. 1, apparatus forcarrying out the process of the invention in a preferred manner is shownto include a storage container 20 from which auxiliary agents such asthe water or alkaline soluble materials and inert fillers are fed to thewet mill 18. The auxiliary agents from wet mill 18 are combined withsynthetic aqueous resin dispersion in container 16 and then fed tostorage container 14. From the container 14 the aqueous resin dispersionis atomized into tablet coating kettle 12 which is set to rotate at anangle so as to effectively tumble the contents thereof. Tablet cores tobe coated are introduced through the cover of the kettle 12 along withdry air. The dry air, after contacting the wet, coated cores absorbswater and exits from the line indicated in the cover of the kettle 12.Coated, dried, finished tablets then move from the kettle 12 to thestorage container 10 from where they can be packaged or otherwisedispensed.

The coating and drying procedure carried out in kettle 12 represents apreferred manner for carrying out the process of the invention. Thus, inkettle 12, tablet cores to be coated are introduced into a rotating,angled tumbling zone. At the same time, aqueous synthetic resindispersion is atomized or sprayed into the tumbling zone so as touniformly and rapidly contact and coat the tablet cores. At the sametime dry air is injected into the tumbling zone. Because of the motionof the zone causing the coated tablets to continually tumble, the dryair thoroughly and quickly contacts the wet coated cores and by thisaction rapidly and efficiently removes the water medium resulting in adried, uniform coating on the tablet cores. Water saturated air iscontinually withdrawn from the tumbling zone 12 to enhance the coatingand drying operation. Thus, by carrying out the coating and dryingoperation as described, using an aqueous dispersion of resin containingfrom 30-60% polymer solids it is possible to efficiently coat tabletcores without having the water medium from the aqueous dispersionadversely affect the cores themselves. Instead, rapid drying in tumblingzone 12 via atomized resin dispersion and the injection of dry airresults in a uniformly coated tablet of high quality.

FIG. 2a is a representation in cross-section of a coated tablet preparedaccording to the present invention. The core of active material isidentified by reference numeral 21 and the tablet coating applied viathe process of the invention is identified by the reference numeral 22.

In FIG. 2b there is shown a microscopic view of a preferred coatingformed according to the process of the invention. The coating is shownto include a continuous porous matrix of polyacrylate formed from a filmforming aqueous synthetic dispersion of polyacrylate. The continuousmatrix is filled with auxiliary agents which in this illustrationinclude talc, tatanium dioxide and milk sugar.

EXAMPLE 1

13 Parts of talc, 1 part of polyethylene glycol (average molecularweight 20,000) and 1 part of tartrazin (foodstuff yellow No. 2, EWG No.E 102) were suspended in 70 parts of demineralized water and, undercontinuous stirring, mixed with 200 parts of an approximately 50%aqueous polyvinyl acetate dispersion ("Mowilith DM1"). The solidscontent of the resulting coating agent amounted to 40.3%.

There was manually applied a quantity of this mixture onto placebo coresrotating in a conventional drageeing kettle so that all of the coreswere moistened. After waiting until the applied liquid had beenuniformly distributed on the moving cores, they were then dried byblowing on of air. As soon as the first layer was dry, which state caneasily be recognized as the cores roll smoothly over one another, thenext layer was applied in the same manner. Following the application ofeight layers, there was obtained a completely unbroken lacquer coatingwhich had a silky gloss, and which required no further treatment. Thetablet cores thereby increased in weight by an average amount of about10%.

EXAMPLE 2

Six parts of talc, 6 parts of saccharose, 3 parts of polyethylene glycol(average molecular weight 20,00) and 1 part of tartrazin were suspendedin 90 parts of demineralized water and mixed, under continuous stirring,with 200 parts of an approximately 50% aqueous polyvinyl acetatedispersion ("Mowilith DM 1"). The solids content of the mixture amountedto 38.2%.

On to placebo cores rotating in a conventional drageeing kettle, therewas applied, using for the spraying a ZDS automatic spraying apparatusaccording to German Pat. No. 1,247,547, several layers of this mixturein such a manner that six layers resulted in a weight increase of thecores of 4-5%. The uniform cores thus obtained, which had a silky gloss,had breakdown times which were as good as those of dragees.

Similar results were obtained with the use of a mixture of 200 parts ofpolyvinyl acetate dispersion ("Mowilith DM 1") and a suspension whichcontained 25 parts of talc, 5 parts of polyethylene glycol (averagemolecular weight 20,000) and 3 parts polyvinyl alcohol ("Mowiol N30-98") in 100 parts of demineralized water.

EXAMPLE 3

Ten parts of saccharose, 5 parts of polyethylene glycol (averagemolecular weight 4,000) and 1 part of Ponceau 6R (foodstuff red No. 1,EWG No. E 126) were dissolved in 125 parts of demineralized water andthen mixed with 200 parts of polyvinyl acetate dispersion ("Mowilith DM1").

This dispersion was sprayed continuously onto placebo cores rotating ina conventional drageeing kettle in an amount which corresponded to about30% of the weight of the cores. Simultaneously, vigorous drying with airwas carried out. In this method of working, it was only necessary totake care that the drying was not too weak. Apart from the waste ofenergy, too strong a drying is not harmful. In this manner, there wereobtained tablets with a single homogeneous coating which constitutedabout 10% of the weight of the cores. The breakdown times thereofcorresponded to those of good dragees.

EXAMPLE 4

Suspensions of the compositions set out in the following Table I wereeach mixed with 200 parts of an aqueous approximately 50% polyvinylacetate dispersion ("Mowilith DM 20").

                  TABLE I                                                         ______________________________________                                        FORMULATION                                                                   NO.            1       2     3     4     5                                    ______________________________________                                        talc           13      10                                                     chalk                        40                                               rice starch                        50    100                                  highly-dispersed silicic                                                      acid ("Acrosil")                   2.5   5                                    saccharose                   5     10    10                                   polyethylene glycol                                                           (average MW 20,000)                                                                          10      10    15    5     20                                   polyvinyl pyrrolidone                                                         ("Kollidon 25")              4     3                                          starch syrup                 5                                                polyvinyl alcohol                                                             ("Mowiol N 30-98")                                                                            5                                                             emulsifying agent                                                             ("Cremophor EL")                   0.5   0.5                                  tartrazin       2                  1     1                                    Ponceau 6R              1    1                                                demineralized water                                                                          150     75    100   130   180                                  ______________________________________                                    

The solids content of the final, mixed coating agents according toformulations 1 to 5 varied between 34 and 46%.

All of the above-described mixtures gave satisfactory coatings. Inparticular, formulations 4 and 5 gave coatings having exceptionally lowbreakdown times which were far superior to those of good dragees.

EXAMPLE 5

100 Parts of talc, 25 parts of polyethylene glycol (average molecularweight 20,000), 0.5 parts of sodium lauryl sulfate, 2 parts of titaniumdioxide and 1 part of tartrazin were suspended in 170 parts ofdemineralized water and the suspension then mixed with 200 parts of anapproximately 50% aqueous polyvinyl propionate dispersion ("Propiofan590 D")

When this mixture was applied to tablet cores using the proceduredescribed in Example 2, there were obtained tablet coatingscharacterized by their good appearance, and which were pharmacologicallysatisfactory.

Satisfactory results were also obtained by mixing 200 parts of the samesynthetic resin dispersion with a suspension of 20 parts of polyethyleneglycol (average molecular weight 4,000), 5 parts of ferric oxide pigmentin 50 parts of demineralized water.

EXAMPLE 6

15 Parts of chalk, 8 parts of saccharose, 0.5 parts of sodium laurylsulfate, 10 parts of titanium dioxide and 60 parts of demineralizedwater were mixed together and then the mixture intimately stirred upwith 200 parts of an approximately 50% aqueous polyvinyl chloridedispersion ("Lutofan 300 D").

By further working according to the method described in Examples 1 and2, there was obtained satisfactory tablet coatings.

EXAMPLE 7

20 Parts of maize starch, 5 parts of polyethylene glycol, 5 parts ofpolyvinyl alcohol ("Mowiol N 30-98"), 3 parts of titanium dioxide, 1part of Ponceau 6R and 90 parts of demineralized water were, insuspended form, mixed with 200 parts of an approximately 50% aqueousdispersion of polyacrylic acid esters ("Acronal 14 D") and the resultingmixture then applied to tablet cores according to the method describedin the preceding Examples. There were thusly obtained pharmacologicallysatisfactory, pink colored tablet coatings which had a good gloss.

Coatings with a different, deeper red color, as well as somewhat shorterbreakdown times, were obtained by admixture of the same synthetic resindispersion with an aqueous suspension of 25 parts of talc, 5 parts ofsaccharose, 5 parts of polyethylene glycol (average molecular weight20,000), 5 parts of ferric oxide pigment and 2 parts of titanium dioxidein 80 parts of demineralized water.

EXAMPLE 8

Example 7 is duplicated using a place of ACRONAL 14 D, EUDRAGIT L 30Dand EUDRAGIT E 30D aqueous polyacrylate dispersions. Good results areobtained.

EXAMPLE 9

20 Parts of talc, 30 parts of chalk, 7 parts of saccharose, 2 parts ofpolyvinyl pyrrolidone ("Kollidon 25"), 10 parts of ferric oxide pigmentwere suspended in 120 parts of demineralized water and mixed with 200parts of an approximately 50% aqueous dispersion of a butadiene-styrenecopolymer ("Litex SB 40").

When this mixture was applied to tablet cores by the method described inExamples 1 or 2, there were obtained pharmacologically satisfactorytablet coatings of good appearance which broke down about as quickly asgood dragees.

What is claimed is:
 1. Coated tablet comprising a core of activematerial soluble in the gastrointestinal tract and a coating surroundingsaid core said coating comprising a continuous porous matrix of asynthetic resin insoluble in the gastrointestinal tract and a water oralkaline soluble material in the pores of said matrix, said coatingbeing formed by applying to said core at least one layer of a coatingcomposition of a film forming aqueous zynthetic resin dispersion with aresin content between 30 and 60% by weight and from 2 to 50% by weightof said water or alkaline soluble material and permitting said coatingcomposition layer to dry, said coated tablet being initially air andmoisture tight.
 2. Coated tablet of claim 1 wherein said water solublematerial is selected from the group consisting of salt, sugar,polyethylene glycol, polyvinyl pyrrolidone and starch syrup.
 3. Coatedtablet of claim 1 wherein said alkaline soluble material is a higherfatty acid.
 4. Coated tablet of claim 1 wherein said alkaline solublematerial is lauric acid.
 5. Coated tablet of claim 1 wherein saidsynthetic resin is a member selected from the group consisting ofpolyvinyl ester, polyvinyl acetal, polyvinyl chloride, butadiene-styrenecopolymer and polyacrylic acid ester.
 6. Coated tablet of claim 1additionally containing an insoluble filler.
 7. Coated tablet of claim 1wherein said insoluble filler is present in an amount of up to 50%referred to the amount of aqueous synthetic resin dispersion.
 8. Coatedtablet of claim 6 wherein said insoluble filler is a member selectedfrom the group consisting of talc, chalk, kaolin, maize starch, richstarch and highly dispersed silicic acid.
 9. Coated tablet of claim 1additionally containing at least one member selected from the groupconsisting of dye stuffs and colored pigments.
 10. Coated tablet ofclaim 1 additionally containing at least one member selected from thegroup consisting of flavoring agents and perservatives.
 11. Coatedtablet of claim 1 additionally containing a plasticizer.
 12. Coatedtablet of claim 11 wherein said plasticizer is a phthalic acid ester.13. Coated tablet of claim 1 wherein said coating comprises 200 parts ofan approximately 50% aqueous polyvinyl acetate dispersion, 13 parts oftalc, 1 part of polyethylene glycol (average molecular weight 20,000) 1part of tartrazin and 70 parts demineralized water.
 14. Coated tablet ofclaim 1 wherein said coating comprises 200 parts of an approximately 50%aqueous polyvinyl acetate dispersion, 6 parts of talc, 6 parts ofsaccharose, 3 parts polyethylene glycol (average molecular weight20,000), 1 part of tartrazin and 90 parts demineralized water. 15.Coated tablet of claim 1 wherein said coating comprises 200 parts of anapproximately 50% aqueous polyvinyl propionate dispersion, 100 partstalc, 25 parts polyethylene glycol (average molecular weight 20,000) 0.5parts sodium lauryl sulfate, 2 parts of titanium dioxide, 1 parttartrazin and 170 parts demineralized water.
 16. Coated tablet of claim1 wherein said coating comprises 200 parts of an approximately 50%aqueous polyvinyl chloride dispersion, 15 parts chalk, 8 partssaccharose, 0.5 parts sodium lauryl sulfate, 10 parts titanium dioxideand 60 parts demineralized water.
 17. Coated tablet of claim 1 whereinsaid coating comprises 200 parts of an approximately 50% aqueousdispersion of polyacrylic acid ester, 20 parts maize starch, 5 partspolyethylene glycol, 5 parts polyvinyl alcohol, 3 parts titaniumdioxide, 1 part Ponceau-6R and 90 parts demineralized water.
 18. Coatedtablet of claim 1 wherein said coating comprises 200 parts of anapproximately 50% aqueous dispersion of a butadiene-styrene copolymer,20 parts talc, 30 parts chalk, 7 parts saccharose, 20 parts polyvinylpyroolidone, 10 parts ferric oxide pigment and 120 parts demineralizedwater.
 19. Coated tablet of claim 1 wherein said coating comprises a 30to 50% aqueous, plasticizer-free acrylic resin dispersion.